CATIA CAD software supports IGES format (.igs, .iges) just fine and can process the data for making new parts (.catpart). If you do not have access to CATIA, then you have to use some kind of other CAD program with CATIA's file type support, or some dedicated CAD / 3D model conversion solution.
Convert IGES 3D exchange format to CATIA part data.
We found 4 software records in the database related to .igs to .catpart file format conversion.
Microsoft Windows software - convert igs to catpart on Windows
A PLM/CAD/CAM/CAE software suite
Convert from igs file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned igs to catpart. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A CAD converter with huge format support
A dedicated CAD converter
A CAD visualizaton, analyzation and translating system